Linear motion guide units have been extensively incorporated in recent years between relatively sliding parts in increased industrial fields including machine tools, various assembling machines, conveyors, and so on. Most prior linear motion guide units have been ordinarily fed with lubricant every a preselected interval based on maintenance schedules to make certain of forming the lubricant film separating the rolling elements from the circulating race, ensuring continuous smooth rolling motion of the rolling elements throughout a circulating circuit. Recently advanced machines and instruments, nevertheless, are increasingly needed to make them virtually maintenance-free from many aspects of conserving energy as well as keeping running cost and maintenance cost of equipment reasonable. Correspondingly, the linear motion guide units incorporated in the advanced machinery, especially the linear motion guide units of the sort of roller bearings are also challenged to keep the consumption of lubricant to a minimum, along with keeping linear motion guide units virtually maintenance free for long-lasting lubrication.
With most conventional linear motion guide units in which the sliders are allowed to travel lengthwise of the elongated guide rail by virtue of more than one rolling element, continuous application of lubricant on or between the load-carrying race and the rolling element is inevitable to continue maintaining an adequate lubricant film between the load-carrying race and the rolling element to keep them against metal-to-metal contact that might otherwise occur, thereby making sure of their high durability.
A linear motion guide system operational with less lubricant supply is disclosed in Japanese Utility Model Laid-Open No. H05-71443, which is envisaged delaying the time interval for lubricant supply into an oil bath, thereby reducing the lubricant supply cycles to simplify lubricant supply operation with accompanying reduced maintenance for lubrication. With the prior linear motion guide unit recited earlier, enclosed lubricant reservoirs fit into their associated recesses cut in the outward surfaces of the forward and aft end caps. The lubricant reservoirs are made to communicate with the turnaround passages of the ball circulating circuit. The lubricant reservoirs are made integrally with spouts that are made to fit into their mating lubricant paths made open to the turnaround passages, leading the lubricant out of the reservoirs into the turnaround passages through their associated mating lubricant paths.
Another Japanese Patent Laid-Open No. H11-22726 discloses a linear motion guide unit in which a slider having a movable body including a table, and so on thereon is allowed to move along a guide rail as more than one ball or roller built in the slider rolls through a circulating circuit. With the prior linear motion guide unit recited earlier, end seals adapted to be secured to forward and aft ends of the slider are each provided therein with a lubricant port and a lubricant groove communicating with the lubricant port while made open to a turnaround passage. A member such as felt adapted to hold and apply the lubricant fits into the lubricant groove, which is rimmed evenly with raised edges to prevent the lubricant from leaking out through between the mating surfaces of the end seal and the associated end of the slider.
The linear motion guide system referred earlier as first example of prior art, nevertheless, is in need of preparing the oil reservoir member to keep any amount of lubricant therein. Moreover, although the oil reservoir member displays intricate configuration in which the spouts are in closer formation to the turnaround passages to make sure of positive seepage of the lubricant out of the oil reservoir member, yet it would be very tough to deliver constantly a desired amount of lubricant in increments. With the linear motion guide unit referred earlier as second example of prior art, yet the member such as felt adapted to hold and apply the lubricant fits into the lubricant groove rimmed around there with raised edges to prevent the lubricant from leaking out through between the mating surfaces of the end seal and the associated end of the slider, the lubricant applicator such as felts alone would be difficult to feed constantly a limited minuscule quantity of lubricant.
Meanwhile, there are two members of the class of linear motion guide units, one of which has balls and the other has cylindrical rollers. With the linear motion guide unit in which cylindrical rollers are selected as the rolling elements, alignment problems to guide rollers in good rolling order without leaning in rolling posture are more encountered, compared with the construction using balls. To cope with this, the cylindrical rollers have to be guided not only on their circular rolling surfaces, but also on their axially opposite end surfaces. Conventionally, there is no linear motion guide unit constructed to meet with an aspect of allowing the rollers to roll through the circulating circuit over a long-lasting service life with adequate application of lubricant, making certain of steady reliability of the maintenance-free on lubricant application. Advanced technology has come to hope a linear motion guide unit which, even though simple in construction in favor of commercial production, is capable of retaining ample lubricant enough to make sure of steady and sustainable lubrication over a long-lasting service life for the cylindrical rollers that roll through a circulating circuit.
On the other side, a linear motion guide unit developed to deal with the problem as stated earlier is disclosed in a commonly-assigned senior Japanese patent application, which was opened to public with Japanese Patent Laid-Open No. 2007-100951 after the Convention priority date of this application and further whose U.S. counterpart was opened under U.S. publication No. 2007-0053619A1. The disclosure of U.S. publication No. 2007-0053619A1 is herein incorporated by reference. The linear motion guide unit was designed to lubricate the rolling elements in the turnaround passages to make sure of positive and sustainable lubrication with the use of simplified lubrication design, with accompanying reduced maintenance for lubrication. In the linear motion guide unit disclosed in the commonly-assigned earlier application, the end cap is made therein with holes starting at the outward end surface and reaching the associated turnaround passage, and further made recessed on the outward end surface thereof. There is provided a lubricant reservoir with raised noses made of a porous compact befitting to impregnation with lubricant. The lubricant reservoir fits into the recess sinking below the outward end surface of the end cap in a formation the raised noses extend through the holes in the end cap to reach the turnaround passage, exposing their tips to the turnaround passage to define in part the curved inside surface of the turnaround passage. The cylindrical rollers as they roll through the turnaround passage are allowed coming into rolling-touch with the exposed noses of the lubricant reservoir, thereby receiving lubricant film from the raised noses of the lubricant reservoir. Thus, the cylindrical rollers are kept better lubrication throughout the circulating circuit.
Though the lubrication design for the cylindrical rollers constructed as stated in the commonly-assigned senior application is befitting to the linear motion guide unit comparatively bulky or large in construction of the class that the cylindrical rollers are selected as the rolling elements, yet it remains a major challenge to develop any lubrication design that is better adaptable for smaller linear motion guide units of the class in which the cylindrical rollers are selected as the rolling elements.